What is Our Lord's favorite virtue?
Faith? Hope? Love? Justice? Or humility?

It is humility. The Little Flower (Saint Thérèse) told us in her own words about humility: "The beginning of all holiness is humbly admitting that without God we can do nothing, but that with, in, and through him, everything is possible."
Jesus became man so that he could save us from the opposite of humility - pride. Pride came into the world through our first parents; they just thought that they could live without God and be happy and wanted to be equal with God.
Remember the words of St. Augustine, "It was pride that caused the fall." If you ask St. Augustine what are the ways to God, he would answer saying: "I would tell you the first is humility, the second is humility, the third is humility..." It is in the very act of incarnation in which Christ humbled himself and became man, and so humility is the favorite virtue of Our Lord.
What is humility? It is to see ourselves as God sees us. It is to know and accept that every good thing we have has come from God as a pure gift to us. We totally depend on him for everything. This is called poverty of the spirit, the first of the eight beatitudes.
The second reason why humility is the favorite of the Lord is because humility is nothing but truth, while pride is nothing but lying. Christ is the way, the truth, and the life. The truth will set us free. If humility is truth, then Christ is humility.

As a religious priest, I pronounced the vows of obedience, chastity, and poverty. When I pronounced these vows, I knelt before my provincial or my superior (it is a position of weakness), placed my hands into his hands, and my superior pronounced the vows aloud to all who were present, binding myself totally and completely to the life of the community and the Church. At St. John's, I give the rest of my life, my desires, my agenda, and my preferences, second only to the commands of the Church.
Psalm 131 has always been my favorite: "Yahweh, my heart has no lofty ambitions, my eyes do not look too high. I am not concerned with great affairs or marvels beyond my scope. Enough for me to keep my soul tranquil and quiet. Like a child in his mother's arms, as content as a child that has been weaned."
Humility, the favorite virtue of the Lord, the cornerstone of growth in God's life, it is the best and most pivotal quality for priestly fidelity and effectiveness. There are obstacles to it, and there are helps to it, but remember: there is no replacement for it!